The squeeze flow behavior of concentrated suspensions of spheres in both Newtonian and 14 shear-thinning fluids is investigated experimentally. Analyzing the evolution of the squeeze force as a function of time for different controlled velocities, the suspension is found to present two main flow regimes. In the first regime the force decreases when the velocity decreases, which is expected and corresponds to a power-law fluid flow of the suspension. In the second regime the force increases when the velocity decreases which is an indication that the suspension is undergoing solid-fluid separation. It is found that the transition between the two regimes is controlled by a Peclet number defined as the ratio of the characteristic time of the fluid filtration through the porous media made up by the particles to the characteristic time of the suspension flow. A phase diagram delimiting the flowability domain under squeeze flow conditions for each suspension can be then determined. In the present study the influence of the theological properties of the continuous phase is particularly investigated. (C) 2004 The Society of Rheology.